1. Field of the Invention
The present invention relates to an ink jet recording medium provided with an ink receiving layer excellent in the ability of preventing the bronzing of ink containing a coloring material and in the ability of fixing the ink. Particularly, the present invention relates to general technologies applicable to an ink jet recording medium excellent in the ability of preventing the bronzing of cyan ink and in the ability for fixing magenta ink.
2. Description of the Related Art
It is currently desired to improve image qualities in an ink jet printer and therefore, studies are being made as to improvements in ink jet recording mediums and also in ink and coloring material themselves. In printers, particularly, developed after the autumn in 2004, a coloring material is used for which the light fastness is predominantly taken into account, a remarkable technological innovation has been observed. As a result, with regard to recent developments in coloring materials, their technical contents have been almost brought together.
For example, materials primarily using carbon black are useful as black ink and materials primarily using D.Y. 132, 92 or the like are useful as yellow ink. These materials are therefore usually used. Also, anthrapyridine type coloring materials obtained from quinacridone type coloring materials which have three or more sulfonic groups as solubilizing groups and are provided with an addition structure such as a triazine ring are used as magenta ink.
Particularly, as cyan ink of a phthalocyanine type coloring material, a phthalocyanine type dye provided with an addition structure such as a triazine ring, having improved light fastness is used. Also, the pigment ink has been centered on the over-placed type with respect to glossy media which leaves many coloring materials on the surface of the media. Therefore, a system is adopted in which a transparent liquid is further added to protect these surface coloring materials.
In the meantime, the ink jet recording medium is generally provided with an ink receiving layer containing an inorganic pigment such as silica particles and alumina hydrate particles held with a polymer binder such as a polyvinyl alcohol. Because usual coloring materials provided to this ink jet recording medium is anionic, a cationic additive is usually added in the ink receiving layer of the ink jet recording medium with the intention of improving the fixability of ink. In many ink receiving layers, a polyvinyl alcohol (hereinafter referred to as “PVA”) having a binder function is used to form a porous structure.
However, there is the case where the cationic additive causes the generation of bronzing.
There is a proposal in Japanese Patent Application Laid-Open No. 2005-262716 for preventing the generation of bronzing in a recording medium provided with two ink receiving layers. In the publication of Japanese Patent Application Laid-Open No. 2005-262716, there is disclosed a recording medium in which the lower layer of the ink receiving layer contains silica, water-soluble zirconium and a cationic polymer and the upper layer of the ink receiving layer contains an alumina hydrate and no cationic compound except the alumina hydrate.
Also, in Japanese Patent Application Laid-Open No. 2002-283708, there is the disclosure that in a recording medium provided with two ink receiving layers, the degree of cationization of the upper ink receiving layer is controlled to be lower than that of the lower ink receiving layer in order to reduce the generation of bronzing.
Moreover, in Japanese Patent Application Laid-Open No. 2004-314635, it is disclosed that an ink jet recording medium is adjusted to pH 8.5 or more to prevent bronzing simply.
Also, a polyallylamine has been used as the cationic additive excellent in ink fixability. In Japanese Patent Application Laid-Open No. H07-266689, Japanese Patent Application Laid-Open No. 2005-154577 and Japanese Patent No. 3683974, there is disclosed an ink jet recording medium using this polyallylamine as the cationic additive.
Japanese Patent Application Laid-Open No. 2005-262716 discloses a structure in which an upper layer coating liquid contains no cationic compound and a lower layer coating liquid contains a cationic compound as the condition required for production. Japanese Patent Application Laid-Open No. 2005-262716 determines that no cationic compound is contained in the upper layer of the ink jet recording medium only from the condition for production. However, the inventors of the present invention have made studies concerning this and as a result, found that the cationic compound added to the lower layer coating liquid (silica dispersion solution) is diffused in the upper-layer-forming coating liquid. This can be proven from the description “bronzing was slightly observed in a part of the colors” in the result of Example 1 of Japanese Patent Application Laid-Open No. 2005-262716. Particularly, 2% by mass of a cationic compound is added in the lower layer coating liquid (silica dispersion solution) in each example, showing that a cationic compound is diffused in the upper layer in all the examples.
In Japanese Patent Application Laid-Open No. 2005-262716, the cyan coloring material used in printers developed before the autumn in 2004 is a usual phthalocyanine dye which is a dye relatively resistant to the bronzing. However, if phthalocyanine dye with improved light fastness is used, the occurrence of a bronzing phenomenon has come to be observed not only, of course, in the ink jet recording medium described in Japanese Patent Application Laid-Open No. 2005-262716 but also in any of the conventional ink jet recording mediums.
In the meantime, a problem has arisen concerning migration in magenta ink. Here, the term “migration” represents a phenomenon that when an ink jet recording medium is allowed to stand in a high-temperature and high-humidity circumstance after ink is used to record, a water-soluble dye migrates in the ink jet recording medium.
In the recording medium using an alumina hydrate in both the upper layer and the lower layer as disclosed in Japanese Patent Application Laid-Open No. 2002-283708, a cationic polymer is contained only in the lower layer. However, the migration of magenta is insufficient.
Particularly, in printers developed after the autumn in 2004, the use of a coloring material is started for which the light fastness is given priority, and therefore, the migration of magenta ink became conspicuous.
As mentioned above, no specific development in the technologies of recording mediums has been made to solve both of the problems concerning (a) the occurrence of bronzing of cyan ink and (b) the generation of migration in magenta ink. This is because if a cationic polymer is added in the ink receiving layer to solve the above problem (b) concerning magenta ink, the cationic polymer exists extending throughout in the direction of the thickness of the ink receiving layer. There is the case where this causes cyan ink to flocculate, which promotes the problem (a) concerning bronzing, bringing about a more serious situation.
Also, in the case of ink using a cyan coloring material with improved flocculation characteristics resulting from the condition that the problem as to an improvement in fastness takes precedence over other problems in current improvements in coloring materials, a bronzing phenomenon tends to occur more conspicuously.
In view of this situation, the inventors of the present invention have made studies concerning the fixing state of each ink in an ink jet recording medium. The inventors have also made studies concerning the fixing state of ink containing an anthrapyridone type coloring material having three or more sulfonic groups or ink containing a phthalocyanine type dye to which a triazine ring is added to improve light fastness. As a result, the following findings have been obtained.
1) It has been clarified that the fixing region in the direction of the depth from the surface of an ink jet recording medium having, as the ink receiving layer, a porous layer containing an alumina hydrate and a binder differs depending on the type of coloring material in the ink. In specific examples, yellow ink, cyan ink and magenta ink were put to the ink receiving layer. As a result, the major fixing region of the yellow ink was present in a range from the surface to a depth of 5 μm or less and the major fixing region of the cyan ink was present in a range of the upper surface part and the vicinity of the surface. Also, the major fixing region of the magenta ink existed in a region relatively deep in the layer and specifically, in a region beyond 15 μm deep from the surface of the ink jet recording medium. In short, it has been found that the fixing region in the direction of the depth in the ink jet recording medium varies depending on the type of coloring material.
2) Such a tendency that the fixing region varies depending on the type of ink is significant with the difference being increased when the ink formed liquid droplets are 5.5 pico liters (preferably 1 pico liter or more) or less in size and particularly small liquid droplets about 2 pico liters. At the same time, a difference in the size of dots formed corresponding to these liquid droplets was observed.
3) Studies made as to the diffusion condition of additives makes it possible to attain the functional separation of the ink receiving layer by localizing the ink fixing region depending on the type of ink in the ink receiving layer. As a result, the above problem has been solved and a novel ink jet recording medium has been provided that can cope to the future trend of the development of coloring materials and is beyond the current technological level.
Specifically, it is a first object to provide a recording medium that can correspond to fixing regions differing in inks or coloring materials in an ink receiving layer and can cope to each characteristic of the coloring materials.
Also, it is a second object to provide an ink jet recording medium that limits the migration of magenta ink preferentially, can preferably attain the prevention of the bronzing of cyan ink at the same time and is excellent in image characteristics.